The present invention relates to an erasing method used in magnetic recording, which can provide rapid and positive erasing without leaving an erasing signal within the video signal frequency band.
There have been proposed a variety of techniques as single-track erasing methods in magnetic recording for video signals, especially in an electronic still camera which uses a floppy disk as a magnetic recording medium. One of these methods is a sweep erasing method. In the sweep erasing method, a track of a magnetic recording medium, for example, a magnetic disk, which has been already written on with a video signal, is first written on with an erasing signal of a frequency within the video signal frequency band (for example, 6 MHz. Then the writing is repeated while continuously increasing the frequency of the erasing signal so that it is finally out of the video signal frequency band. Since the frequency of the erasing signal written on the track by the sweep erasing method is out of the video signal frequency band, the recorded erasing signal can be easily cut off by a filter at reproduction so that only the necessary video signal can be reproduced. Thus, the originally recorded video signal is substantially erased by overwriting the track containing the original video signal with a number of erasing signals of different frequencies. In this case, the video signal recorded in the deep layer of the magnetic recording medium is erased by the erasing signals of relatively lower frequencies, and the video signal recorded in the surface layer is erased by the erasing signals of relatively higher frequencies.
The prior art sweep erasing method, however, has a problem in that if the erasing time is reduced (for example, less than 2 seconds), the erasing signals remain unerased within the video signal frequency band, with a higher noise level than a method which uses a bulk eraser for erasing.